[Susceptibility of guinea pig eyes to form deprivation myopia and its age-related recovery].

OBJECTIVE: Young guinea pigs are susceptible to become myopic during form deprivation. They can also quickly recover from the myopia after removal of the form deprivation. This study investigated whether mature guinea pigs are sensitive to form deprivation and its refractive recovery from deprivation myopia. METHODS: It was an experimental study. Thirty-nine guinea pigs were arranged to 3 groups according to age. Group 1: 9-week old (n = 18). Group 2: 12-week old (n = 10). Group 3: 15-week old (n = 11). All the animals were performed refraction measurement prior to the experiment, then wore a facemask that covered one randomly assigned eye for three weeks. The masks were then removed and refraction was measured in both eyes immediately, 2 and 7 days after. RESULTS: After form deprivation, the refraction of the MFD (monocular form deprivation) eyes shifted to myopia, which had significant difference compared to the unmasked eye in all the groups (t = -5.691, -2.203, -2.760; P < 0.05), the relative myopia compared to the unmasked eye in 9 weeks old animals were (-2.53 ± 1.89) D, 12 weeks old (-1.43 ± 1.57) D, 15 weeks old (-0.60 ± 1.48) D. There was significant difference between 9 weeks old animals and 15 weeks old animal in the refractive error right after the form deprivation (F = 2.823, P < 0.05). And the distribution of refractive error tended to lower degree of myopia as the guinea pigs grew older. None of the three groups showed significant reduction in relative refractive error during the recovery, but a trend of recovery was found in 9 weeks old animals. CONCLUSIONS: The guinea pigs are sensitive to the form deprivation even when they are sexual mature, but both the susceptibility and the ability of recovery decrease as they grow older but in different patterns. The ability of recovery in short term (7 days) diminishes when guinea pig is older than 12 weeks while the sensitivity to form deprivation last until 15 w.

Interactions of chromatic and lens-induced defocus during visual control of eye growth in guinea pigs (Cavia porcellus).

It was recently demonstrated that chromaticity could affect eye growth and refractive development in guinea pigs but it remained unclear whether correction with spectacle lenses could balance these effects and how retinal responses change with different spectral compositions of light. Three illumination conditions were tested: blue, red and white light. Animals were raised without or with monocular spectacle lenses from three to seven weeks of age. Luminance electroretinograms (ERGs) were recorded to explore retinal responses with the different spectral compositions. In our special colony of pigmented guinea pigs, characterized by residual hyperopia, spontaneous myopia and poor emmetropization, red light induced early thinning of the choroid and relative myopia, compared to white light. Effects of red light could not be suppressed if positive spectacle lenses were worn. ERGs showed that red light failed to elicit robust retinal responses. Blue light inhibited axial eye growth, even when animals were reared with negative lenses. Intensity-matched blue and white light elicited similar a-waves but different b-waves, suggesting that the wavelength of light affects visual control of eye growth through different processing in the inner retina. We hypothesize that blue light might stimulate preferentially the ON pathway to inhibit myopia induced by negative lenses, at least in guinea pigs.

The effect of temporal and spatial stimuli on the refractive status of guinea pigs following natural emmetropization.

PURPOSE: To understand the visual information essential for maintaining stable refraction after emmetropization, we investigated the effects of spatial and temporal stimuli on the refractive status of guinea pigs. METHODS: Eighty-eight guinea pigs (4 weeks old) were randomly divided into 10 groups. Thirty animals were raised in backgrounds of gray (N = 13), square-wave (N = 9), or sine-wave grating (N = 8). Thirty-one animals were raised in gray backgrounds with three frequencies of flicker: gray-1-Hz (n = 10), gray-6-Hz (n = 12), and gray-20-Hz (n = 9). Eighteen animals were raised in regular cages with different frequencies of flicker (n = 6 respectively in 1-Hz-, 6-Hz-, and 20-Hz-flicker groups). Nine animals were raised in regular cages with no additional stimuli and used as normal controls. Ocular biometry was measured before and after 3 weeks of exposure to the test environments. RESULTS: Guinea pigs raised in the gray background for 3 weeks developed myopia, -6.1 ± 2.1 diopters (D), whereas those exposed to either sine-wave or square-wave gratings, or raised in regular cages, retained stable refractions. Animals in the gray-6-Hz group developed lower myopia, -2.7 ± 2.7 D, than the gray group not exposed to flicker. Animals stimulated with a range of flickering frequencies in regular cages also developed myopia but to a lower degree, -3.1 to 0.2 D, than those in gray backgrounds, -5.0 to -2.7 D. CONCLUSIONS: Guinea pigs require both spatial and temporal stimuli to maintain stable refractions. The influence of temporal stimuli on refraction varies with the type and amount of spatial information available in the visual environment.